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Saffren, M. M.

Publications and source records attributed to Saffren, M. M..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Closed loop electrostatic levitation system

An electrostatic levitation system is described, which can closely control the position of objects of appreciable size. A plurality of electrodes surround the desired position of an electrostatically charged object, the position of the objects is monitored, and the voltages applied to the electrodes are varied to hold the object at a desired position. In one system, the object is suspended above a plate-like electrode which has a concave upper face to urge the object toward the vertical axis of the curved plate. An upper electrode that is also curved can be positioned above the object, to assure curvature of the field at any height above the lower plate. In another system, four spherical electrodes are positioned at the points of a tetrahedron, and the voltages applied to the electrodes are varied in accordance with the object position as detected by two sensors.

Rhim, W. K.↗
NASA NTRS1983

Electrostatic Levitator With Feedback Control

Sample position automatically maintained. Object levitated by electrostatic field between two electrodes. Because of particular curved electrode shape, levitation field has stable horizontal position on vertical axis of symmetry. Vertical position of object sensed and compared with preset value. When position error is detected, amplitude of levitating field is increased or decreased to restore zero error. System offers options well to containerless processing.

Rhim, W. K.↗
NASA NTRS1983

Theory of Compound Liquid Drops

Dynamic behavior is analyzed for drop within drop within infinite fluid. Report gives theoretical basis for understanding behavior of compound drops. Aids in planning and interpreting experiments in laboratory, spacecraft, and research aircraft. Provides insight into fabrication of target pellets for nuclear fusion.

Saffren, M. M.↗
NASA NTRS1982

Development of electrostatic levitator at JPL

Preliminary results on the design and operation of electrostatic levitators developed at JPL are reported. Particular attention is given to the single-axis levitators for ground-based operation and for operation in the reduced gravity environment. Descriptions are given of the design principles and the performance of final products. A levitator designed for zero-g environment is shown. It is a single-axis system, so there is no active lateral damping. Two ring and two disk electrodes are included. The ring electrodes always maintain a constant voltage difference with respect to the central disk electrodes. This is to ensure that there is always a centering force that does not depend on the voltage difference between the top and bottom electrodes. As the ring-to-disk voltage increases, there is a proportionate increase in the centering force.

Rhim, W.-K.↗
NASA NTRS1981

Characterization of superfluid helium transfer

The friction factor and steady state flow rate of superfluid helium (He II) are measured, with the driving pressure difference generated by the saturated vapor pressure and a small hydrostatic pressure head. The temperature ranged from 1.5 K to the transition temperature of 2.17 K. Three different lengths and two different internal diameters were used for the stainless steel transfer tubes, and the transfer of liquid helium (He I) was investigated with the same apparatus for comparison. It was found that the friction factor of He II is greater than that of He I for pressure differences greater than 20 mm Hg, and smaller below that magnitude.

Yang, L. C.↗
NASA NTRS1977

Apparatus for photon excited catalysis

An apparatus is described for increasing the yield of photonically excited gas phase reactions by extracting excess energy from unstable, excited species by contacting the species with the surface of a finely divided solid.

Saffren, M. M.↗
NASA NTRS1977

Drop dynamics in space

Experiments to study the dynamics of liquid drops are being planned to be performed in the weightless environment of Spacelab. The liquids will range from superfluid helium through ordinary liquid to molten metals and glasses. The experiments will be conducted in a chamber now being developed which utilizes the forces and torques produced by acoustic waves excited within the chamber. None of the currently available facilities (drop towers, sounding rockets, or zero-g aircraft flights) can provide a sustained weightless environment, since the resulting zero-g periods are from 3 sec to 5 min. Spaceflight, however, will provide weightlessness for periods of one week, or more, allowing truly laboratory-like experiments to be conducted on free liquid drops and bubbles. In this paper we discuss both the drop dynamics experiments proposed for Spacelab and the acoustic chamber: its operation and current testing for these and other experiments.

Wang, T. G.↗
NASA NTRS1976

Drop dynamics in space

Drop experiments proposed for Spacelab are discussed and an acoustic chamber utilizing the torques and forces produced by acoustic waves excited within the chamber is described. Its operation and how it is being tested for experiments is discussed.

Wang, T. G.↗
NASA NTRS1976

Method and apparatus for generating coherent radiation in the ultra-violet region and above by use of distributed feedback

Helium in the superfluid state emits copious amounts of radiation in the ultraviolet region when excited by an electron stream. Conventional laser action using mirrors is impossible in superfluid helium because there are no mirrors that will reflect VUV radiation. By utilizing the distributed feedback method, the superfluid helium can be made to lase. By setting up a standing wave in superfluid helium that has a wavelength equal to, or harmonically related to, half the wavelength of the photon radiation chosen to be emitted as laser radiation by the superfluid helium, the need for end mirrors to produce reflection of the laser radiation is eliminated and reflection occurs instead at the wavefronts of the standing wave. The photons leave the superfluid helium at right angles to the standing wave as coherent radiation having a very high intensity. The standing wave established in the superfluid helium may be an acoustical standing wave, a thermal standing wave (second sound), or an electric standing wave.

Saffren, M. M.↗
NASA NTRS1975

Heat-operated cryogenic electrical generator

Generator operation is based upon unusual hydrodynamic properties exhibited by liquid helium below superfluid critical point. Below that temperature, liquid behaves as though it is mixture of two interpenetrating fluids. When transition takes place between superfluid and normal states, conservation of momentum is always balanced by normal fluid.

Wang, T. G.↗
NASA NTRS1975

High-energy lasers by using distributed reflection: A concept

Lasers may be made with higher energy photons than heretofore possible. It has been proposed that vacuum ultraviolet lasing can be obtained by bombarding superfluid helium with electron beam, while coupling acoustic energy into helium to set up standing waves in fluid.

Saffren, M. M.↗
NASA NTRS1975

Material suspension within an acoustically excited resonant chamber

A method is described for positioning an object within a chamber, which is especially useful in performing manufacturing operations under zero gravity conditions. Sound waves are applied within the chamber in different directions and at a frequency for each direction that establishes a standing wave pattern so that the object is automatically urged towards the intersections of the nodes, or locations of minimum pressure.

Wang, T. G.↗
NASA NTRS1975

Heat operated cryogenic electrical generator

An electrical generator useful for providing electrical power in deep space, is disclosed. The electrical generator utilizes the unusual hydrodynamic property exhibited by liquid helium as it is converted to and from a superfluid state to cause opposite directions of rotary motion for a rotor cell thereof. The physical motion of the rotor cell was employed to move a magnetic field provided by a charged superconductive coil mounted on the exterior of the cell. An electrical conductor was placed in surrounding proximity to the cell to interact with the moving magnetic field provided by the superconductive coil and thereby generate electrical energy. A heat control arrangement was provided for the purpose of causing the liquid helium to be partially converted to and from a superfluid state by being cooled and heated, respectively.

Wang, T. G.↗
NASA NTRS1974

Onset phenomena in superfluid helium

Onset phenomena in superfluid helium have been studied by measuring the rotational decay constant of a levitated, superconducting niobium sphere coated with an unsaturated superfluid film. The novel features of onset that were observed are discussed. Previous observations of a two-layer-thick solid phase of helium underlying the film have been confirmed.

Wang, T. G.↗
NASA NTRS1974

Acoustical levitation for space processing

It is pointed out that many space-manufacturing processes will require the manipulation of weightless molten material within a container in such a way that the material does not touch the container wall. A description is given of an acoustical method which can be used for the positioning and shaping of any molten material including nonconductors such as glasses. The new approach makes use of an acoustical standing wave which is excited within an enclosure or resonator.

Wang, T. G.↗
NASA NTRS1974

Acoustical positioning chamber for space processing

By readily levitating, positioning, and manipulating materials placed in it, the acoustical resonator can serve a variety of space processing operations, such as drawing crystals, degassing, and stirring of melts, and casting.

Wang, T. G.↗
NASA NTRS1974

Acoustic chamber for weightless positioning

The objective of this work is to perfect and extend the acoustic position technique that was developed at JPL for use in the future Space Processing Laboratory in Space. The main effort is centered on design of a position device for processing of molten materials. Namely, a resonator has the capability of positioning in an extreme temperature gradient and a frequency servo loop to maintain it there as the temperature varies.

Wang, T. G.↗